The present invention relates to a position measuring device having a graduated scale carrier member which is secured to a holder.
Position measuring devices of this kind are used, in particular, on machine tools for measuring the relative position of a tool with respect to a workpiece. The graduated scale carrier member is either directly adhesively mounted on an object, such as a machine part to be measured, or is secured to this object by way of a holder, for example one that at the same time constitutes a housing. It has become apparent that the measuring accuracy of a position measuring device is substantially dependent upon the mounting attachment of the graduated scale carrier member to the object to be measured.
To optimize this attachment, in accordance with German Patent 196 11 983 C1, a viscous liquid film is used between the graduated scale carrier member and the holder. The capillary action of the viscous intermediate layer provides for the coupling between the graduated scale carrier member and the holder, and it substantially uncouples the graduated scale carrier member from the holder with respect to occurring mechanical strains.
The disadvantage of this arrangement is that the scale graduation marking of the graduated scale carrier member lies completely exposed.
To solve this problem, the European Patent 0 416 391 B1describes a position measuring device, whose graduated scale carrier member is made of glass, and which is secured to the holder by its side bearing on the scale graduation marking by way of a viscous liquid film. The scale graduation marking is scanned through the transparent glass carrier.
In this arrangement, the scale graduation marking is accommodated in a manner in which it is very well protected from environmental influences. The drawback of the system, however, is that the graduated scale carrier member itself is exposed to all environmental influences. Because of the relatively large distance of the scale graduation marking from the neutral fiber of the graduated scale carrier member, the graduation-marking bearing surface is considerably expanded or compressed under the influence of external mechanical forces causing an uneven supporting base. The resulting scale error is relatively significant.
The present invention is a position measuring device, whose graduated scale carrier member is substantially uncoupled from its holder with respect to mechanical strains, and is also protected in a simple manner from external mechanical influences.
In one embodiment, the invention is a position measuring device comprising a graduated scale carrier member, a measuring graduation marking disposed on the graduated scale carrier member, a holder having a first surface facing the measuring graduation marking, the holder being adhesively secured to the graduated scale carrier member by an elastic intermediate film, and a scanning unit for scanning the measuring graduation marking to produce positionally dependent signals, the scanning unit being disposed adjacent a second surface of the holder, opposite the first surface. The measuring graduation marking is disposed opposite to the scanning unit, and is scannable by the scanning unit through the holder.
The present invention provides the benefit that, using simple means, the scale graduation marking is effectively protected from impurities and from external mechanical influences, so that this position measuring device can be used for performing highly precise measurements.
Other advantages, which are derived from advantageous embodiments of the present invention, are delineated in the following description.